I've been using Playback (DLNA server) to convert MKV files with 5.1 AC3 to MP4 and every time I do it the audio downsamples to 2 channel AAC. The good folks at Yazsoft said that Perian is responsible for the conversion process, they just provide the interface. I can't figure out why this is happening as they claim to be successfully converting these files with AC3 5.1. Is there a way to troubleshoot this? A fix perhaps?

They do control what conversion is done. It sounds like you are wanting a stream passthrough for audio (5.1 AC3 -> 5.1 AC3). If their software is capable of doing this, it will not use Perian for anything in that process. If they insist that Perian is used in that passthrough, then they don't know what they are talking about.

Again:

gbooker wrote:If they were doing a stream copy, Perian wouldn't enter into the picture at all.

Regardless of what they say, Perian is not at issue here; so you need to talk with them. They are using Perian to convert from 5.1 AC3 -> PCM, and then from PCM -> AAC (this step is not in Perian). Perian is doing exactly what it is told here, so you if your complaint is that it is downsampled to 2 channel AAC, Perian is only enabling this because Playback told it to do so. So again: